First impressions are sometimes our only impressions. It may be important to judge a person based on their capabilities, but your appearance says a great number of things nonverbally that might surprise you. For business in general, the below might have some useful information concerning the importance of your dress.
The General Idea
For males, you should at least come in slacks and a button-up shirt that is buttoned. Tucked in would be preferable to left hanging, but it is not a highly important factor. Full suits with ties are the most formal one should wear.
For females, a conservative dress is typically seen as acceptable. Pants and blouse are also an option, similar to the male outfit.
For both genders, jewelry should be kept to a minimum, and do not go overboard on cologne or perfume.
Interviews: The Beginning
How you appear in front of an interviewer can indicate the perception you have of their business. For example, if someone were to appear to a scheduled interview in sweatpants, an attention getting shirt, and no care taken with regards to hair, then the interviewer is likely to assume you did not put much effort into your preparation.
Some people have the misconception that you need to be extravagant and make an impression in order to get hired. While it is good to be noticed, going overboard is very easy to do. Use your words, resume, and the interview to make the impression, instead of opting for an extreme outfit that is more likely to have the interviewer call the cops than their boss.
Others believe that conforming to the standards of business or society is compromising themselves as a person. If you have long hair and bear, then you do not need to go and get a standard haircut and be completely clean shaven. Instead show that you at least care about the impression you make by styling your hair in a conservative manner and careful grooming. This would allow such a person to keep their general persona while achieving a suitable business appearance.
Continue the Trend
Once you have established your dedication and professionalism, you may not have to dress the same way for that business every time you go to work. This may make it seem like your efforts were just to conform to an unspoken standard, and that is because it is the truth. If your job does expect the appearance daily, it will be up to you to maintain a presentation of decorum and sensibility.